QSFP28 Cables and Transceivers for Data Center Upgrade

četvrtak , 23.02.2017.

Since the 10G/40G Ethernet network can not satisfy the development of the fiber technology, data centers around the world spare no effort to explore preferable options for higher network speed and larger bandwidth. The 100G Ethernet network was published under that situation, and accordingly, a series of related solutions like QSFP28 cables and QSFP28 transceivers are designed for data center upgrade. In fact, QSFP28 cables and QSFP28 transceivers are not the most popularly used but also useful solutions, with the aim of upgrading 10G/40G Ethernet network to 100G Ethernet network, which will be studied in the this post.

QSFP28 Solutions
QSFP28 cables like QSFP28 DACs and QSFP28 AOCs and QSFP28 transceivers like QSFP28 SR4 and QSFP28-LR4 are the widely used solutions for data center upgrade, both of which highly surpass their corresponding traditional devices, such as, QSFP+ cables and QSFP+ transceivers. For the detailed information about these QSFP28 cables and QSFP28 transceivers, let’s explore them in the following text.

QSFP28 Cables

QSFP28 cables are the cost-efficient solutions to deal with the issues caused by connecting cables with transceivers, which are able to support the 100G Ethernet network by directly connecting 100G devices together. Thereby, with the use of QSFP28 cables, a lot of connection issues can be eliminated or avoided and the whole 100G connection can be accomplished easily and fast.

At present, the QSFP28 cables can be simply divided into direct-attach copper cables (DACs) and active optical cables (AOCs), as shown in the following figure. As for the QSFP28 DACs, they can be available at the lowest cost, while only suitable for the applications within 15m transmission distance. They are easily found in the racks of the data center and can be also used for chassis-to-chassis interconnect in large switch and routers. As for the QSFP28 AOCs, they are much lighter than the QSFP28 DACs. What’s more, the QSFP28 AOC can transmit the 100G signal with a much longer distance, 100 m or even more.

QSFP28 Transceivers

Compared to the QSFP28 cable mentioned above, QSFP28 transceiver could be much more complicated which is implemented with four 25-Gbps lanes for achieving 100G transmission. QSFP28 transceiver is the smallest 100G form factor transceiver that has the exact same footprint and faceplate density as 40G QSFP+ transceiver. Although it keeps the physical dimension of its predecessor, it has a great improvement in the panel density and also highly decreases power consumption. From the figure below, you can learn the two common types of QSFP28 transceivers, QSFP28 SR4 and QSFP28 LR4.



As for the QSFP28 SR4 transceiver, it came into the market firstly to transmit the 100G signal through multimode fiber (MMF) for a short transmission distance. In details, 100G signal supported by the QSFP28 SR4 transceiver can be transmitted through OM3 MMF at length up to 70 m, while 100 m through OM4 MMF. Meanwhile, it features with MTP interface, which allows for 4×25G dual way transmission over 8 fibers.

Clearly different from the QSFP28 SR4 transceiver, QSFP28 LR4 transceiver is specifically designed for 100G long distance transmission, as the letter L (long) in its name implies. This kind of QSFP28 module with duplex LC interface always works on single-mode fiber (SMF), supporting the 100G dual-way transmission up to 10 km. When it is working, WDM technology will be used for the 4×25G signals long transmission, and each 25G signal will be transmitted over four different wavelengths.

Conclusion
From this paper, you can learn two kinds of commonly used QSFP28 cable solutions, QSFP28 DAC and QSFP28 AOC. QSFP28 DAC is always used for 100G short distance transmission, within 15 m, while QSFP28 AOC is a good choice for 100G longer transmission, up to 100 m or even more. You can also learn two kinds of commonly used QSFP28 transceiver solutions, QSFP28 SR4 transceiver and QSFP28 LR4 transceiver which are much complicated for deploying the 100G network. The former one always works with MMF for short distance transmission, but the latter one can support the 100G network for a long distance. Besides, there are more QSFP28 solutions shown in the article, which may be more useful for you to upgrade your system.